Arrays

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8

• Arrays

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Now go, write it before them in a table, and
note it in a book. Isaiah 308
To go beyond is as wrong as to fall
short. Confucius
Begin at the beginning, and go on till you come
to the end then stop. Lewis Carroll
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OBJECTIVES

• In this chapter you will learn
• What arrays are.
• To use arrays to store data in and retrieve data
  from lists and tables of values.
• To declare arrays, initialize arrays and refer to
  individual elements of arrays.
• To use the foreach statement to iterate through
  arrays.
• To pass arrays to methods.
• To declare and manipulate multidimensional
  arrays.
• To write methods that use variable-length
  argument lists.
• To read command-line arguments into an
  application.

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• 8.1   Introduction
• 8.2   Arrays
• 8.3   Declaring and Creating Arrays
• 8.4   Examples Using Arrays
• 8.5   Case Study Card Shuffling and Dealing
  Simulation
• 8.6   foreach Statement
• 8.7   Passing Arrays and Array Elements to
  Methods
• 8.8   Passing Arrays by Value and by Reference
• 8.9   Case Study Class GradeBook Using an Array
  to Store Grades
• 8.10   Multidimensional Arrays
• 8.11   Case Study Class GradeBook Using a
  Rectangular Array
• 8.12   Variable-Length Argument Lists
• 8.13   Using Command-Line Arguments
• 8.14   (Optional) Software Engineering Case
  Study Collaboration Among Objects in the ATM
  System
• 8.15   Wrap-Up

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Fig. 8.1 A 12-element array.
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Common Programming Error 8.1

• In an array declaration, specifying the number of
  elements in the square brackets of the
  declaration (e.g., int 12  c) is a syntax
  error.

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Good Programming Practice 8.1

• For readability, declare only one variable per
  declaration. Keep each declaration on a separate
  line and include a comment describing the
  variable being declared.

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Outline
InitArray.cs
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Outline
InitArray.cs
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Good Programming Practice 8.2

• Constants also are called named constants. Such
  variables often make applications more readable
  than applications that use literal values (e.g.,
  10)a named constant such as ARRAY_LENGTH clearly
  indicates its purpose, whereas a literal value
  could have different meanings based on the
  context in which it is used. Another advantage to
  using named constants is that if the value of the
  constant must be changed, it is necessary to
  change it only in the declaration, thus reducing
  the cost of maintaining the code.

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Outline
InitArray.cs (1 of 2)
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Outline
InitArray.cs (2 of 2)
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Common Programming Error 8.2

• Assigning a value to a named constant after it
  has been initialized is a compilation error.

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Common Programming Error 8.3

• Attempting to declare a named constant without
  initializing it is a compilation error.

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Outline
SumArray.cs
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Outline
BarChart.cs (1 of 2)
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Outline
BarChart.cs (2 of 2)
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Outline
RollDie.cs
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Outline
StudentPoll.cs (1 of 2)
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Outline
StudentPoll.cs (2 of 2)
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Error-Prevention Tip 8.1

• An exception indicates that an error has occurred
  in an application. You often can write code to
  recover from an exception and continue
  application execution, rather than abnormally
  terminating the application. Exception handling
  is discussed in Chapter 12.

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Error-Prevention Tip 8.2

• When writing code to loop through an array,
  ensure that the array index remains greater than
  or equal to 0 and less than the length of the
  array. The loop-continuation condition should
  prevent the accessing of elements outside this
  range.

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Outline
Card.cs
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Outline
DeckOfCards.cs (1 of 2)
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Outline
DeckOfCards.cs (2 of 2)
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Outline
DeckOfCardsTest.cs (1 of 2)
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Outline
DeckOfCardsTest.cs (2 of 2)
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Outline
ForEachTest.cs
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Outline
PassArray.cs (1 of 3)
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Outline
PassArray.cs (2 of 3)
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Outline
PassArray.cs (3 of 3)
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Performance Tip 8.1

• Passing arrays and other objects by reference
  makes sense for performance reasons. If arrays
  were passed by value, a copy of each element
  would be passed. For large, frequently passed
  arrays, this would waste time and would consume
  considerable storage for the copies of the
  arraysboth of these problems cause poor
  performance.

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Outline
ArrayReferenceTest.cs (1 of 5)
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Outline
ArrayReferenceTest.cs (2 of 5)
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Outline
ArrayReferenceTest.cs (3 of 5)
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Outline
ArrayReferenceTest.cs (4 of 5)
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Outline
ArrayReferenceTest.cs (5 of 5)
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Software Engineering Observation 8.1

• When a method receives a reference-type parameter
  by value, a copy of the objects reference is
  passed. This prevents a method from overwriting
  references passed to that method. In the vast
  majority of cases, protecting the callers
  reference from modification is the desired
  behavior. If you encounter a situation where you
  truly want the called procedure to modify the
  callers reference, pass the reference-type
  parameter using keyword refbut, again, such
  situations are rare.

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Software Engineering Observation 8.2

• In C, objects (including arrays) are passed by
  reference by default. So, a called method
  receiving a reference to an object in a caller
  can change the callers object.

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Outline
GradeBook.cs (1 of 6)
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Outline
GradeBook.cs (2 of 6)
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Outline
GradeBook.cs (3 of 6)
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Outline
GradeBook.cs (4 of 6)
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Outline
GradeBook.cs (5 of 6)
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Outline
GradeBook.cs (6 of 6)
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Software Engineering Observation 8.3

• A test harness (or test application) is
  responsible for creating an object of the class
  being tested and providing it with data. This
  data could come from any of several sources. Test
  data can be placed directly into an array with an
  array initializer, it can come from the user at
  the keyboard, it can come from a file (as you
  will see in Chapter 18) or it can come from a
  network (as you will see in Chapter 23). After
  passing this data to the classs constructor to
  instantiate the object, the test harness should
  call the object to test its methods and
  manipulate its data. Gathering data in the test
  harness like this allows the class to manipulate
  data from several sources.

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Outline
GradeBookTest.cs (1 of 2)
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Outline
GradeBookTest.cs (2 of 2)
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Fig. 8.17 Rectangular array with three rows
and four columns.
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Fig. 8.18 Jagged array with three rows of
different lengths.
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Outline
InitArray.cs (1 of 3)
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Outline
InitArray.cs (2 of 3)
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Outline
InitArray.cs (3 of 3)
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Outline
GradeBook.cs (1 of 7)
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Outline
GradeBook.cs (2 of 7)
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Outline
GradeBook.cs (3 of 7)
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Outline
GradeBook.cs (4 of 7)
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Outline
GradeBook.cs (5 of 7)
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Outline
GradeBook.cs (6 of 7)
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Outline
GradeBook.cs (7 of 7)
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Outline
GradeBookTest.cs (1 of 2)
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Outline
GradeBookTest.cs (2 of 2)
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Outline
VarargsTest.cs (1 of 2)
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Outline
VarargsTest.cs (2 of 2)
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Common Programming Error 8.4

• Using the params modifier with a parameter in the
  middle of a method parameter list is a syntax
  error. The params modifier may be used only with
  the last parameter of the parameter list.

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Outline
InitArray.cs (1 of 3)
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Outline
InitArray.cs (2 of 3)
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Outline
InitArray.cs (3 of 3)
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Fig. 8.24 Collaborations in the ATM system.
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Fig. 8.25 Communication diagram of the ATM
executing a balance inquiry.
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Fig. 8.26 Communication diagram for executing
a BalanceInquiry.
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Fig. 8.27 Sequence diagram that models a
Withdrawal executing.
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Fig. 8.28 Sequence diagram that models a
Deposit executing.